Switching converters are widely used in the field of power conversion. A switching converter includes at least one switch that is configured to generate a pulse-width modulated (PWM) voltage from an input voltage, and a rectifier arrangement that receives the PWM voltage and generates an output voltage to be supplied to a load. Usually the rectifier arrangement includes at least one inductive storage element, such as a choke, and at least one capacitive storage element, such as a capacitor. The PWM voltage is generated by switching the switching element on and off in accordance with a PWM drive signal. The drive signal is provided by a controller dependent on the output voltage. The controller is configured to vary the duty cycle of the drive signal in order to control the output voltage such that it assumes a given set-voltage.
The duty cycle of the drive signal is dependent on a power consumption of the load, whereas the duty cycle increases when the power consumption increases, and the duty cycle decreases when the power consumption decreases. Under low-load conditions, which is when a power consumption of the load is very low, modern controllers enter a burst mode. In the burst mode the switching element is cyclically switched on and off during a burst-on period, and the switching element is permanently in an off-state during a burst-off period subsequent to the burst-on period. The burst-on period and the burst-off period define a burst period TBP and a burst frequency fBP, where fBP=1/TBP. The burst frequency is dependent on several parameters, such as the input voltage, and the power consumption of the load.
Problems may occur when the burst frequency is in a frequency range of between 1 kHz and 4 kHz. A burst frequency in this range may cause an annoying audible noise. There is, therefore, a need to prevent the generation of an audible noise when a switching converter is operated in its burst mode.